Intra Prediction For Multi-Hypothesis

ABSTRACT

A video decoder that decodes a current block of pixels by using multi-hypothesis combined prediction mode is provided. The video decoder generates a first prediction of the current block based on an inter prediction mode. The video decoder enables the combined prediction mode for the current block based on a block size of the current block determined according to a width and a height of the current block. The combined prediction mode is disabled when the width of or the height of the current block is greater than a threshold length. When the combined prediction mode is enabled, the video decoder generates a second prediction based on an intra prediction mode that is inferred to be a planar mode, and subsequently a combined prediction for the current block based on the first prediction and the second prediction. The video decoder reconstructs the current block by using the combined prediction.

CROSS REFERENCE TO RELATED PATENT APPLICATION(S)

The present disclosure is part of a non-provisional application thatclaims the priority benefit of U.S. Provisional Patent Application No.62/744,464, filed on 11 Oct. 2018. Contents of above-listed applicationsare herein incorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to video processing. Inparticular, the present disclosure relates to methods of coding a pixelblock by using multiple hypothesis to perform inter prediction.

BACKGROUND

Unless otherwise indicated herein, approaches described in this sectionare not prior art to the claims listed below and are not admitted asprior art by inclusion in this section.

High-Efficiency Video Coding (HEVC) is an international video codingstandard developed by the Joint Collaborative Team on Video Coding(JCT-VC). HEVC is based on the hybrid block-based motion-compensatedDCT-like transform coding architecture. The basic unit for compression,termed coding unit (CU), is a 2N×2N square block, and each CU can berecursively split into four smaller CUs until the predefined minimumsize is reached. Each CU contains one or multiple prediction units(PUs).

To achieve the best coding efficiency of hybrid coding architecture inHEVC, there are two kinds of prediction modes for each PU, which areintra prediction and inter prediction. For intra prediction modes, thespatial neighboring reconstructed pixels can be used to generate thedirectional predictions. There are up to 35 directions in HEVC. Forinter prediction modes, the temporal reconstructed reference frames canbe used to generate motion compensated predictions. There are threedifferent modes, including Skip, Merge and Inter Advanced Motion VectorPrediction (AMVP) modes.

When a PU is coded in Inter AMVP mode, motion-compensated prediction isperformed with transmitted motion vector differences (MVDs) that can beused together with Motion Vector Predictors (MVPs) for deriving motionvectors (MVs). To decide MVP in Inter AMVP mode, the advanced motionvector prediction (AMVP) scheme is used to select a motion vectorpredictor among an AMVP candidate set including two spatial MVPs and onetemporal MVP. So, in AMVP mode, MVP index for MVP and the correspondingMVDs are required to be encoded and transmitted. In addition, the interprediction direction to specify the prediction directions amongbi-prediction, and uni-prediction which are list 0 (L0) and list 1 (L1),accompanied with the reference frame index for each list should also beencoded and transmitted.

When a PU is coded in either Skip or Merge mode, no motion informationis transmitted except the Merge index of the selected candidate. That isbecause the Skip and Merge modes utilize motion inference methods(MV=MVP+MVD where MVD is zero) to obtain the motion information fromspatially neighboring blocks (spatial candidates) or a temporal block(temporal candidate) located in a co-located picture where theco-located picture is the first reference picture in list 0 or list 1,which is signaled in the slice header. In the case of a Skip PU, theresidual signal is also omitted. To determine the Merge index for theSkip and Merge modes, the Merge scheme is used to select a motion vectorpredictor among a Merge candidate set containing four spatial MVPs andone temporal MVP.

SUMMARY

The following summary is illustrative only and is not intended to belimiting in any way. That is, the following summary is provided tointroduce concepts, highlights, benefits and advantages of the novel andnon-obvious techniques described herein. Select and not allimplementations are further described below in the detailed description.Thus, the following summary is not intended to identify essentialfeatures of the claimed subject matter, nor is it intended for use indetermining the scope of the claimed subject matter.

Some embodiments of the disclosure provide a video decoder that decodesa current block of pixels by using multi-hypothesis (MH) combinedprediction mode. The MH combined prediction mode includes at least oneof MH mode for intra and MH mode for inter. The video decoder generatesa first prediction of the current block based on an inter predictionmode. The video decoder enables the combined prediction mode for thecurrent block based on a block size of the current block determinedaccording to a width and/or a height of the current block. The combinedprediction mode is disabled when the width of the current block or theheight of the current block is greater than a threshold length. Thethreshold can be a fixed value or based on the max TU (e.g., 64)specified in the standard, or the maximum TU size (e.g., 64) specifiedin SPS/PPS/tile/tile group/slice level. When the combined predictionmode is enabled, the video decoder generates a second prediction basedon an intra prediction mode or inter prediction mode and a combinedprediction for the current block based on the first prediction and thesecond prediction. The video decoder reconstructs the current block byusing the combined prediction.

In some embodiments, the video decoder performs a simplified intraprediction when generating the second prediction based on the intraprediction mode. The video decoder generates the second prediction byusing the intra prediction mode to identify a set of neighboring pixelsand applying an interpolation filter to the identified set ofneighboring pixels to produce a set of interpolated pixels. In someembodiments, the set of interpolated pixels is used as the secondprediction without further improvement. In some embodiments, the secondprediction is computed without using position dependent intra predictioncombination (PDPC) or angular intra prediction. When the intraprediction mode is planar mode, the second prediction is computed byomitting at least one of (i) reference availability check andsubstitution, (ii) reference sample filtering, (iii) horizontal planarpredictor generation and averaging, and (iv) PDPC.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present disclosure and are incorporated in andconstitute a part of the present disclosure. The drawings illustrateimplementations of the present disclosure and, together with thedescription, serve to explain the principles of the present disclosure.It is appreciable that the drawings are not necessarily in scale as somecomponents may be shown to be out of proportion than the size in actualimplementation in order to clearly illustrate the concept of the presentdisclosure.

FIG. 1 shows the MVP candidates set for inter-prediction modes in HEVC.

FIG. 2 illustrates a merge candidates list that includes combinedbi-predictive merge candidates.

FIG. 3 illustrates a merge candidates list that includes scaled mergecandidates.

FIG. 4 illustrates an example in which zero vector candidates are addedto a merge candidates list or an AMVP candidates list.

FIG. 5 shows the intra-prediction modes in different directions.

FIG. 6 illustrates a four parameter affine motion model.

FIG. 7 illustrates MVP derivation for affine inter mode.

FIG. 8 a conceptually illustrates encoding or decoding a block of pixelsby using Multi-hypothesis mode for Intra.

FIG. 8 b conceptually illustrates encoding or decoding a block of pixelsby using Multi-hypothesis mode for Inter.

FIG. 9 conceptually illustrates enabling MH mode for Intra or MH modefor inter based on size, width, or height of pixel blocks.

FIG. 10 illustrates an example video encoder that may implement MH modefor intra or MH mode for inter.

FIG. 11 a illustrates portions of the video encoder that may implementMH mode for intra when encoding a block of pixels.

FIG. 11 b illustrates portions of the video encoder that may implementMH mode for inter when encoding a block of pixels.

FIG. 12 conceptually illustrates a process that encodes a block ofpixels using MH mode for intra or MH mode for inter.

FIG. 13 illustrates an example video decoder that may implement MH modefor intra or MH mode for inter.

FIG. 14 a illustrates portions of the video decoder that may implementMH mode for intra when decoding a block of pixels.

FIG. 14 b illustrates portions of the video decoder that may implementMH mode for inter when decoding a block of pixels.

FIG. 15 each conceptually illustrates a process that decodes a block ofpixels using MH mode for Intra or MH mode for Inter.

FIG. 16 conceptually illustrates an electronic system with which someembodiments of the present disclosure are implemented.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth by way of examples in order to provide a thorough understanding ofthe relevant teachings. Any variations, derivatives and/or extensionsbased on teachings described herein are within the protective scope ofthe present disclosure. In some instances, well-known methods,procedures, components, and/or circuitry pertaining to one or moreexample implementations disclosed herein may be described at arelatively high level without detail, in order to avoid unnecessarilyobscuring aspects of teachings of the present disclosure.

Inter-Prediction Modes

FIG. 1 shows the MVP candidates set for inter-prediction modes in HEVC(i.e., skip, merge, and AMVP). The figure shows a current block 100 of avideo picture or frame being encoded or decoded. The current block 100(which can be a PU or a CU) refers to neighboring blocks to derive thespatial and temporal MVPs for AMVP mode, merge mode or skip mode.

For skip mode and merge mode, up to four spatial merge indices arederived from A₀, A₁, B₀ and B₁, and one temporal merge index is derivedfrom T_(BR) or T_(CTR) (T_(BR) is used first, if T_(BR) is notavailable, T_(CTR) is used instead). If any of the four spatial mergeindex is not available, the position B₂ is used to derive merge index asa replacement. After the deriving four spatial merge indices and onetemporal merge index, redundant merge indices are removed. If the numberof non-redundant merge indices is less than five, additional candidatesmay be derived from original candidates and added to the candidateslist. There are three types of derived candidates:

1. Combined bi-predictive merge candidate (derived candidate type 1)

2. Scaled bi-predictive merge candidate (derived candidate type 2)

3. Zero vector merge/AMVP candidate (derived candidate type 3)

For derived candidate type 1, combined bi-predictive merge candidatesare created by combining original merge candidates. Specifically, if thecurrent slice is a B slice, a further merge candidate can be generatedby combining candidates from List 0 and List 1. FIG. 2 illustrates amerge candidates list that includes combined bi-predictive mergecandidates. As illustrated, two original candidates having mvL0 (themotion vector in list 0) and refldxL0 (the reference picture index inlist 0) or mvL1 (the motion vector in list 1) and refldxL1 (thereference picture index in list 1), are used to create bi-predictiveMerge candidates.

For derived candidate type 2, scaled merge candidates are created byscaling original merge candidates. FIG. 3 illustrates a merge candidateslist that includes scaled merge candidates. As illustrated, an originalmerge candidate has mvLX (the motion vector in list X, X can be 0 or 1)and refldxLX (the reference picture index in list X, X can be 0 or 1).For example, an original candidate A is a list 0 uni-predicted MV withmvL0_A and reference picture index ref0. Candidate A is initially copiedto list L1 as having reference picture index ref0′. The scaled MVmvL0′_A is calculated by scaling mvL0_A based on ref0 and ref0′. Ascaled bi-predictive Merge candidate having mvL0_A and ref0 in list L0and mvL0′_A and ref0′ in list L1 is created and added to the mergecandidates list. Likewise, a scaled bi-predictive merge candidate whichhas mvL1′_A and ref1′ in List 0 and mvL1_A, ref1 in List 1 is createdand added to the merge candidates list.

For derived candidate type 3, zero vector candidates are created bycombining zero vectors and reference indices. If a created zero vectorcandidate is not a duplicate, it is added to the merge/AMVP candidateslist. FIG. 4 illustrates an example in which zero vector candidates areadded to a merge candidates list or an AMVP candidates list.

Intra-Prediction Mode

Intra-prediction method exploits one reference tier adjacent to thecurrent prediction unit (PU) and one of the intra-prediction modes togenerate the predictors for the current PU. The Intra-predictiondirection can be chosen among a mode set containing multiple predictiondirections. For each PU coded by Intra-prediction, one index will beused and encoded to select one of the intra-prediction modes. Thecorresponding prediction will be generated and then the residuals can bederived and transformed.

FIG. 5 shows the intra-prediction modes in different directions. Theseintra-prediction modes are referred to as directional modes and do notinclude DC mode or Planar mode. As illustrated, there are 33 directionalmodes (V: vertical direction; H: horizontal direction), so H, H+1˜H+8,H−1˜H−7, V, V+1˜V+8, V−1˜V−8 are used. Generally directional modes canbe represented as either as H+k or V+k modes, where k=±1, ±2, . . . ,±8. (In some embodiments, intra-prediction mode has 65 directional modesso that the range of k is from ±1 to ±16.)

Out of the 35 intra-prediction modes in HEVC, 3 modes are considered asthe most probable modes (MPM) for predicting the intra-prediction modein current prediction block. These three modes are selected as an MPMset. For example, the intra-prediction mode used in the left predictionblock and the intra-prediction mode used in the above prediction blockare used as MPMs. When the intra-prediction modes in two neighboringblocks use the same intra-prediction mode, the intra-prediction mode canbe used as an MPM. When only one of the two neighboring blocks isavailable and coded in directional mode, the two neighboring directionsimmediately next to this directional mode can be used as MPMs. DC modeand Planar mode are also considered as MPMs to fill the available spotsin the MPM set, especially if the above or top neighboring blocks arenot available or not coded in intra-prediction, or if theintra-prediction modes in neighboring blocks are not directional modes.If the intra-prediction mode for current prediction block is one of themodes in the MPM set, 1 or 2 bits are used to signal which one it is.Otherwise, the intra-prediction mode of the current block is not thesame as any entry in the MPM set, and the current block will be coded asa non-MPM mode. There are all-together 32 such non-MPM modes and a(5-bit) fixed length coding method is applied to signal this mode.

In some embodiments, position dependent intra prediction combination(PDPC) is applied to some of the intra modes without signaling: planar,DC, horizontal, vertical, bottom-left angular mode and its x adjacentangular modes, and top-right angular mode and its x adjacent angularmodes. The value x depends on the number of angular modes. Descriptionsof PDPC can be found in: G. Van der Auwera, J. Heo, A. Filippov, “CE3:Summary Report on Intra Prediction and Mode Coding,” 11th JVET Meeting,Ljubljana, SI, July 2018, JVET-K0023; ITU-T SG16/Q6 Doc. COM16-C1046,“Position Dependent intra Prediction Combination (PDPC)”; X. Zhao, V.Seregin, A. Said, M. Karczewicz, “EE1 related: Simplification andextension of PDPC”, 8th JVET Meeting, Macau, Oct. 2018, JVET-H0057; andM. Karczewicz et al., “Description of SDR, HDR and 360° video codingtechnology proposal by Qualcomm,” 10th JVET Meeting, San Diego, Calif.,USA, Apr. 2018, JVET-J0021.

Affine Merge Mode

HEVC uses only translation motion model for motion compensationprediction. There are many other types of motions in the real world,such as zoom-in and zoom-out, rotation, perspective motions, and otherirregular motions. Some of these other types of motions may berepresented by affine transformation or affine motion, which preservespoints, straight lines and planes. An affine transformation does notnecessarily preserve angles between lines or distances between points,but it does preserve ratios of distances between points lying on astraight line. When an affine motion block is moving, the motion vectorfield of the block can be described by two control point motion vectorsor four parameters as the following:

The transformed block is a rectangular block. The motion vector field ofeach point in this moving block can be described by the followingequation:

$\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0y}}}\end{matrix} \right.$

Where (v_(0x), v_(0y)) is the control point motion vector on top leftcorner, and (v_(1x), v_(1y)) is another control point motion vector onabove right corner of the block. In some embodiments, for a inter modecoded CU, when the CU size is equal to or larger than 16×16, anaffine_flag is signaled to indicate whether the affine inter mode isapplied or not. If the current CU is in affine inter mode, a candidateMVP pair list is built using the neighbor valid reconstructed blocks.FIG. 6 illustrates a four parameter affine motion model.

FIG. 7 illustrates MVP derivation for affine inter mode. As shown inFIG. 7 , the v₀ is selected from the motion vectors of the block A₀, A₁or A₂, and the v₁ is selected from the motion vectors of the block B₀and B₁. The index of candidate MVP pair is signaled in the bit stream.The MV difference (MVD) of the two control points are coded in thebitstream.

In some embodiments, if the current PU is a merge PU, the neighboringfive blocks (C0, B0, B1, C1, and A0 blocks in FIG. 7 ) are checkedwhether one of them is affine inter mode or affine merge mode. If yes,an affine_flag is signaled to indicate whether the current PU is affinemode. When the current PU is coded in affine merge mode, the first blockis coded by affine mode from valid neighbor reconstructed blocks. Theselection order for the candidate block is from left, above, aboveright, left bottom to above left (C0→B0→B1→C1→A0) as shown in FIG. 7 .The affine parameter of the first affine coded block is used to derivethe v₀ and v₁ for the current PU.

Ultimate Motion Vector Expression (UMVE)

In some embodiments, ultimate motion vector expression (UMVE) is usedfor either skip or merge modes. When a candidate is selected from amongthe merge candidates, the expression of the selected candidate isexpanded under UMVE. UMVE provides a motion vector expression withsimplified signaling. The UMVE motion vector expression includesprediction direction information, starting point, motion magnitude, andmotion direction.

In some embodiments, a merge candidate list is used as it is. However,candidates that are default merge type (MRG_TYPE_DEFAULT_N) areconsidered for UMVE's expansion. In UMVE expansion, the Predictiondirection information indicates a prediction direction among L0, L1, andL0 and L1 predictions. In B slice, the bi-prediction candidates can begenerated from merge candidates with uni-prediction by using mirroringtechnique. For example, if a merge candidate is uni-prediction with L1,a reference index of L0 is decided by searching a reference picture inlist 0, which is mirrored with the reference picture for list 1. Ifthere is no corresponding picture, the nearest reference picture to thecurrent picture is used. L0′ MV is derived by scaling L1's MV. Thescaling factor is calculated by picture order count (POC) distance.

If the prediction direction of the UMVE candidate is the same with oneof the original merge candidates, the index with value 0 is signaled asan UMVE prediction direction. But, if not the same (same with one of theoriginal merge candidates), the index with value 1 is signaled. Aftersending first bit, remaining prediction direction is signaled based onthe pre-defined priority order of UMVE prediction direction. Priorityorder is L0/L1 prediction, L0 prediction and L1 prediction. If theprediction direction of merge candidate is L1, signaling ‘0’ is forUMVE′ prediction direction L1. Signaling ‘10’ is for UMVE′ predictiondirection L0 and L1. Signaling ‘11’ is for UMVE′ prediction directionL0. If L0 and L1 prediction lists are same, UMVE's prediction directioninformation is not signaled.

Base candidate index defines the starting point. Base candidate indexindicates the best candidate among candidates in the list as follows.

TABLE 1 Base candidate Index Base candidate 0 1 2 3 IDX

TABLE 2 Distance Index Distance IDX 0 1 2 3 4 5 6 7 Pixel ¼-pel ½-pell-pel 2-pel 4-pel 8-pel 16-pel 32-pel distance

Direction index represents the direction of the MVD relative to thestarting point. The direction index can represent of the four directionsas shown below.

TABLE 3 Direction IDX Direction IDX 00 01 10 11 x-axis + — N/A N/Ay-axis N/A N/A + —

In some embodiments, to reduce encoder complexity, block restriction isapplied. For example, if either width or height of a CU is less than 4,UMVE is not performed.

Multi-Hypothesis Mode

Some embodiments of the disclosure provide a Multi-hypothesis mode toimprove Inter prediction, which is an improved method for Skip and/orMerge modes. In original Skip and Merge mode, one Merge index is used toselect one motion candidate, which may be either uni-prediction orbi-prediction derived by the candidate itself, from the Merge candidatelist. The generated motion compensated predictor is referred to as thefirst hypothesis (or first prediction) in some embodiments. UnderMulti-hypothesis mode, a second hypothesis is produced in addition tothe first hypothesis. The second hypothesis of predictors can begenerated by motion compensation from a motion candidate based on aninter prediction mode, (e.g., Merge or Skip modes), or by intraprediction based on an intra prediction mode.

When Multi-hypothesis mode is supported, one or more Multi-hypothesiscandidate(s) may be available for Skip and/or Merge mode. When thesecond hypothesis (or second prediction) is generated by an Intraprediction mode, the Multi-hypothesis mode is referred to as MH mode forIntra or MH mode Intra or MH Intra. When the second hypothesis isgenerated by motion compensation by a motion candidate or an interprediction mode (e.g., Merge or Skip mode), the Multi-hypothesis mode isreferred to as MH mode for Inter or MH mode Inter or MH Inter (or alsocalled as MH mode for Merge or MH Merge).

For Multi-hypothesis mode, each Multi-hypothesis candidate (or calledeach candidate with Multi-hypothesis) contains one motion candidate(i.e., first hypothesis) and one prediction mode (i.e., secondhypothesis), where the motion candidate is selected from Candidate ListI and the prediction mode is selected from Candidate List II. For someembodiments for MH mode for intra, each Multi-hypothesis candidate (orcalled each candidate with Multi-hypothesis) contains one motioncandidate and one Intra prediction mode, where the motion candidate isselected from Candidate List I and the intra prediction mode is selectedfrom Candidate List II. That is, one motion candidate may match one ormore intra prediction mode(s) at the encoder (or one or more motioncandidates may match one intra prediction mode at the encoder); andthrough encoding mode decision, one motion candidate and one intraprediction mode is decided and signaled to the decoder.

For some embodiments for MH mode for Inter, each Multi-hypothesiscandidate contains two motion candidates and at least one of the twomotion candidates are selected from Candidate List I. In someembodiments, Candidate List I is identical to the Merge candidates listof the current block and that both motion candidates of aMulti-hypothesis candidate of MH mode for inter are selected fromCandidate List I. In some embodiments, the Candidate List I is a subsetof the Merge candidate list. In some embodiments, one of the motioncandidates of a Multi-hypothesis candidate is selected from the Mergecandidate list and another one of the motion candidates of the sameMulti-hypothesis candidate is selected from Candidate List I.

FIG. 8 a conceptually illustrate encoding or decoding a block of pixelsby using MH Mode for Intra. The figure illustrates a video picture 800that is currently being encoded or decoded by a video coder. The videopicture 800 includes a block of pixels 810 that is currently beingencoded or decoded as a current block. The current block 810 is coded byMH mode for intra, specifically, a combined prediction 820 is generatedbased on a first prediction 822 (first hypothesis) of the current block810 and a second prediction 824 (second hypothesis) of the current block810. The combined prediction 820 is then used to reconstruct the currentblock 810.

The current block 810 being coded by using MH mode for Intra.Specifically, the first prediction is obtained by inter-prediction basedon at least one of reference frames 802 and 804. The second predictionis obtained by intra-prediction based on neighboring pixels 806 of thecurrent block 810. As illustrated, the first prediction 822 is generatedbased on an inter-prediction mode or a motion candidate 842 (firstprediction mode) that is selected from a first candidate list 832(Candidate List I) comprising one or more candidate inter-predictionmodes. The second prediction 824 is generated based on anintra-prediction mode 844 (second prediction mode) that is selected froma second candidate list 834 (Candidate List II) comprising one or morecandidate intra-prediction modes.

FIG. 8 b illustrates the current block 810 being coded by using MH modefor Inter. Specifically, the first prediction 822 is obtained byinter-prediction based on at least one of reference frames 802 and 804.The second prediction 824 is obtained by inter-prediction based on atleast one of reference frames 806 and 808. As illustrated, the firstprediction 822 is generated based on an inter-prediction mode or amotion candidate 842 (first prediction mode) that is selected from thefirst candidate list 832 (Candidate List I). The second prediction 824is generated based on an inter-prediction mode or a motion candidate 846(second prediction mode) that is also selected from the first candidatelist 832 (Candidate List I).

In some embodiments, when MH mode for Intra is supported, one flag issignaled (for example, to represent whether MH mode for Intra isapplied). Such a flag may be represented or indicated by a syntaxelement in a bitstream. In some embodiment, if the flag is on, oneadditional Intra mode index is signaled to indicate the Intra predictionmode from Candidate List II. In some embodiment, if the flag is on, theintra prediction mode for MH mode for intra is implicitly selected fromCandidate List II.

In some embodiments, for MH mode for Intra or MH mode for Inter, theindices that are used to select the first prediction mode and the secondprediction mode are separately and distinctly signaled, e.g., as twosyntax elements in a bitstream that encodes the video picture 800. Forexample, a first syntax element may be used to indicate the selection ofthe first candidate 842 from the first candidate list 832 and a secondsyntax element may be used to indicate the selection of the secondcandidate 844 from the second candidate list 834 (or the first candidatelist 832).

In some embodiments, for MH mode for Intra, the indices that are used toselect the first prediction mode is signaled, e.g., as one syntaxelements in a bitstream that encodes the video picture 800. For example,a first syntax element may be used to indicate the selection of thefirst candidate 842 from the first candidate list 832 and the secondcandidate 844 from the second candidate list 834 (or the first candidatelist 832) is decided implicitly.

In some embodiments, different variance of MH mode for intra or MH modefor inter may be implemented by the video coder according to thedifferent settings such as supported-mode setting, combined-weightsetting, intra mode settings, block size settings, and any combinationof above. The selection of a MH mode for Intra or MH mode for intersetting can be implicitly derived by the block width and/or block heightor be explicitly indicated by a flag signaled at CU level, CTU level,slice level, tile level, tile group, SPS level, or PPS level or be anycombination of above.

Supported-Mode Settings

A hypothesis of intra prediction or inter prediction may be combinedwith a hypothesis of inter prediction from different inter modes (thatare identified by the supported-mode setting). In some embodiments, onehypothesis of inter prediction can be generated from any one of existinginter modes, such as skip, merge, AMVP, affine merge, affine AMVP, orsub-block merge. In some embodiments, MH mode for intra can support animproved inter mode. For example, UMVE candidates can be used togenerate one hypothesis of inter prediction. For another example, themotion information used to generate a hypothesis of inter prediction canbe acquired through referencing previous coded motion information in ahistory-based scheme (or called as history-based motion vectorprediction (HMVP)). HMVP candidate is defined as the motion informationof a previously coded block. A table with multiple HMVP candidates ismaintained during the encoding/decoding process. The table is emptiedwhen a new slice is encountered.

Combined-Weight Settings:

Weightings are used to combine the multiple hypotheses of prediction forMH mode for intra or MH mode for inter (e.g., for computing a weightedsum of the first hypothesis of prediction and the second hypothesis ofprediction as the combined prediction). The weightings may be fixed at aparticular value or may vary with the block width or block height or apredefined lookup table. For example, an equal weighting can be appliedto multiple hypotheses of prediction.

Intra Mode Settings:

Candidate List II can be determined according to intra mode setting.When the size of Candidate List II (the number of candidates in thelist) is equal to one, the selected intra mode can be inferred to be theonly one available intra prediction mode in the Candidate List IIwithout signaling. For example, Candidate List II may include onlyplanar mode, and the selected intra mode is inferred to be planar mode.

In some embodiments, Candidate List II consists of any one or anycombination of {Planar, DC, horizontal, Diagonal} or any one or anycombination of {Planar, DC, horizontal, Diagonal} ±offset, where theoffset is an integer. In some embodiments, (the candidates of the)Candidate List II varies with the block size or block width or blockheight. In some embodiments, planar mode is absent from Candidate ListII. Any combination of above can be applied to MH mode for intra. In oneexample, when the block size is smaller than a particular threshold,denoted as T, where T can be 4×4, 8×8, 16×16, 32×32, Candidate List IIincludes more than one intra prediction modes, which can be anycombination of {Planar, DC, horizontal, Diagonal} or any combination of{Planar, DC, horizontal, Diagonal} ±offset. In another example, when theblock size is larger than a particular threshold, denoted as T, where Tcan be 4×4, 8×8, 16×16, 32×32, Candidate List II may include any one orany combination of {DC, horizontal, Diagonal} or any one or anycombination of {DC, horizontal, Diagonal} ±offset. One benefit ofremoving planar mode from Candidate List II for larger blocks is toreduce the size of a buffer that is used to generate the hypothesis ofintra prediction. The threshold can be a fixed value or based on the maxTU (e.g. 64) specified in the standard, or the maximum TU size (e.g. 64)specified (for example, parsed or signaled) in SPS/PPS/tile/tilegroup/slice level.

In some embodiments, the intra prediction process of MH mode for intracan be aligned with or identical to the intra prediction process fornormal intra mode (normal intra mode being an intra mode that is not tobe combined with inter prediction as part of multi-hypothesis predictionor normal intra mode being an intra mode described in the section:intra-prediction mode). In some embodiment, the intra prediction processof MH mode for intra can be a simplified version of the intra predictionprocess of normal intra modes. The simplification scheme (or thesimplified intra prediction process of MH mode for intra) may omit (atleast some of) the filtering process, reduce the length of intrainterpolation filter, omit the tools for improving intra prediction suchas PDPC, wide angular intra prediction (proposed in JVET-K0500), etc.For example, a simplified planar mode (for simplified intra prediction)may apply part (or a subset) or none of these four planar predictionsteps: (1) reference sample availability check and substitution, (2)reference sample filtering, (3) horizontal and vertical planar predictorgeneration and averaging, and (4) PDPC, whereas normal planar mode mayinclude all four planar prediction steps.

Block Size Settings:

Multi-hypothesis mode (for example, MH mode for intra and/or MH mode forinter) may be enabled according to the block width and/or block heightof the current block. In some embodiments, MH mode for intra can bedisabled (or called forbidden) for a block with size larger than aparticular threshold such as 4×4, 8×8, 16×16, 32×32, 64×64, or 128×128.One benefit of disabling or forbidding MH mode for intra for largerblocks is to reduce the size of a buffer for generating the hypothesisof intra prediction. In some embodiments, MH mode for intra can bedisabled (or called forbidden) for a block with size smaller than aparticular threshold such as 4×4, 8×8, 16×16, or 32×32. (In other words,MH mode for Intra can be enabled for a bock with size larger than orequal to the particular threshold such as 4×4, 8×8, 16×16, or 32×32). Insome embodiment, MH mode for intra can be disabled (or called forbidden)for the block with the block width larger than N and/or the block heightlarger than M, where N and M can be 4, 8, 16, 32, 64, or 128. Anycombination of above can be applied to MH mode for intra. In someembodiments, N×M can be represented as a block size threshold generatedby the result of N×M. For example, for when the block area is largerthan 16, 32, 64, 128, 256, 512, or 1024, MH mode for Intra or MH modefor Inter is disabled (or called forbidden). For example, for the blockarea smaller than 16, 32, 64, 128, 256, 512, or 1024, MH mode for Intraor MH mode for inter is disabled (or called forbidden). In someembodiment, the proposed block size setting can be used for MH mode forinter. In some embodiments, when MH mode for intra or MH mode for interis disabled (or called forbidden), the syntax (e.g. a flag indicatingwhether the current block is encoded using MH mode for intra in theencoded video data) for the disabled mode (which can be MH mode forintra or MH mode for inter) is not signaled at encoder and not parsed atdecoder. In some embodiments, when the syntax (e.g. a flag indicatingwhether the current block is encoded using MH mode for intra in theencoded video data) for the disabled mode (which can be MH mode forintra or MH mode for inter) is not signaled at encoder and not parsed atdecoder, the syntax is inferred to be false and the disabled mode is notapplied.

FIG. 9 conceptually illustrates enabling Multi-hypothesis mode (forexample, MH mode for Intra and/or MH mode for inter) based on size,width, or height of pixel blocks. A video coder is encoding or decodinga video picture 900. The video picture 900 is partitioned into blocks ofvarious sizes, including 4×4 blocks 911-914, 8×8 blocks 921-923, 16×16blocks 931-933, a 32×32 block 941, and a 128×32 block 951.

Some of the blocks are CUs or PUs that are split from a larger CU byquad splitting, binary splitting, ternary splitting, etc. The videocoder determines a block size of the current block according to a widthof the current block, a height of the current block or both. In someembodiments, the video coder enables MH mode for Intra (or MH mode forinter) for the current block based on the block size of the currentblock. MH mode for Intra (or MH mode for inter) is disabled when thewidth of the block is greater than a threshold width or when the heightof the block is greater than a threshold height. In some embodiments, MHmode for Intra (or MH mode for inter) is disabled when the width or theheight of the block is greater than a threshold length.

The video coder enables Multi-hypothesis mode (for example, MH mode forIntra and/or MH mode for inter) for coding a block if the size of theblock is 8×8. Take the MH mode for Intra for example, the MH mode forIntra has an enabling threshold of block size 64. The video coderdisables MH mode for Intra (or MH mode for inter) for coding the blockif the width or the height of the block is greater than 64, e.g., the MHmode for Intra has a disabling threshold length, width, or height >64.Blocks for which MH mode for intra is enabled are illustrated asunshaded, while blocks for which MH mode for intra is disabled areillustrated as shaded. As illustrated, blocks 911-914 are not coded byMH mode for intra because their widths and heights do not result in ablock size larger than or equal to the enabling threshold of 8×8 or 64.Blocks 921-923, 931-933, and 941 have sizes that meet the enablingthreshold of 64, so MH mode for Intra may be enabled for coding theseblocks. The Block 951 has a width 128 that is larger than the disablingthreshold of 64, so MH mode for Intra is disabled for coding the block951.

Any of the foregoing proposed methods can be implemented in encodersand/or decoders. For example, any of the proposed methods can beimplemented in an inter coding module or intra coding module of anencoder, a motion compensation module, a merge candidate derivationmodule of a decoder. Alternatively, any of the proposed methods can beimplemented as a circuit coupled to the inter coding module or intracoding module of an encoder and/or motion compensation module, a mergecandidate derivation module of the decoder.

Example Video Encoder

FIG. 10 illustrates an example video encoder 1000 that may implement MHmode (MH mode for Intra and/or MH mode for Inter). As illustrated, thevideo encoder 1000 receives input video signal from a video source 1005and encodes the signal into bitstream 1095. The video encoder 1000 hasseveral components or modules for encoding the signal from the videosource 1005, including at least part of a transform module 1010, aquantization module 1011, an inverse quantization module 1014, aninverse transform module 1015, an intra-picture estimation module 1020,an intra-prediction module 1025, a motion compensation module 1030, amotion estimation module 1035, an in-loop filter 1045, a reconstructedpicture buffer 1050, a MV buffer 1065, and a MV prediction module 1075,and an entropy encoder 1090. The motion compensation module 1030 and themotion estimation module 1035 are part of an inter-prediction module1040.

In some embodiments, the modules 1010-1090 are modules of softwareinstructions being executed by one or more processing units (e.g., aprocessor) of a computing device or electronic apparatus. In someembodiments, the modules 1010-1090 are modules of hardware circuitsimplemented by one or more integrated circuits (ICs) of an electronicapparatus. Though the modules 1010-1090 are illustrated as beingseparate modules, some of the modules can be combined into a singlemodule.

The video source 1005 provides a raw video signal that presents pixeldata of each video frame without compression. A subtractor 1008 computesthe difference between the raw video pixel data of the video source 1005and the predicted pixel data 1013 from the motion compensation module1030 or intra-prediction module 1025. The transform module 1010 convertsthe difference (or the residual pixel data or residual signal 1009) intotransform coefficients (e.g., by performing Discrete Cosine Transform(DCT), Discrete Sine Transform (DST) or any other transform function).The quantization module 1011 quantizes the transform coefficients intoquantized data (or quantized coefficients) 1012, which is encoded intothe bitstream 1095 by the entropy encoder 1090.

The inverse quantization module 1014 de-quantizes the quantized data (orquantized coefficients) 1012 to obtain transform coefficients, and theinverse transform module 1015 performs inverse transform on thetransform coefficients to produce reconstructed residual 1019. Thereconstructed residual 1019 is added with the predicted pixel data 1013to produce reconstructed pixel data 1017. In some embodiments, thereconstructed pixel data 1017 is temporarily stored in a line buffer(not illustrated) for intra-picture prediction and spatial MVprediction. The reconstructed pixels are filtered by the in-loop filter1045 and stored in the reconstructed picture buffer 1050. In someembodiments, the reconstructed picture buffer 1050 is a storage externalto the video encoder 1000. In some embodiments, the reconstructedpicture buffer 1050 is a storage internal to the video encoder 1000.

The intra-picture estimation module 1020 performs intra-prediction basedon the reconstructed pixel data 1017 to produce intra prediction data.The intra-prediction data is provided to the entropy encoder 1090 to beencoded into bitstream 1095. The intra-prediction data is also used bythe intra-prediction module 1025 to produce the predicted pixel data1013.

The motion estimation module 1035 performs inter-prediction by producingMVs to reference pixel data of previously decoded frames stored in thereconstructed picture buffer 1050. These MVs are provided to the motioncompensation module 1030 to produce predicted pixel data.

Instead of encoding the complete actual MVs in the bitstream, the videoencoder 1000 uses MV prediction to generate predicted MVs, and thedifference between the MVs used for motion compensation and thepredicted MVs is encoded as residual motion data and stored in thebitstream 1095.

The MV prediction module 1075 generates the predicted MVs based onreference MVs that were generated for encoding previously video frames,i.e., the motion compensation MVs that were used to perform motioncompensation. The MV prediction module 1075 retrieves reference MVs fromprevious video frames from the MV buffer 1065. The video encoder 1000stores the MVs generated for the current video frame in the MV buffer1065 as reference MVs for generating predicted MVs.

The MV prediction module 1075 uses the reference MVs to create thepredicted MVs. The predicted MVs can be computed by spatial MVprediction or temporal MV prediction. The difference between thepredicted MVs and the motion compensation MVs (MC MVs) of the currentframe (residual motion data) are encoded into the bitstream 1095 by theentropy encoder 1090.

The entropy encoder 1090 encodes various parameters and data into thebitstream 1095 by using entropy-coding techniques such ascontext-adaptive binary arithmetic coding (CABAC) or Huffman encoding.The entropy encoder 1090 encodes various header elements, flags, alongwith the quantized transform coefficients 1012, and the residual motiondata as syntax elements into the bitstream 1095. The bitstream 1095 isin turn stored in a storage device or transmitted (for example,transmitted to a decoder over a communications medium such as anetwork).

The in-loop filter 1045 performs filtering or smoothing operations onthe reconstructed pixel data 1017 to reduce the artifacts of coding,particularly at boundaries of pixel blocks. In some embodiments, thefiltering operation performed includes deblocking or sample adaptiveoffset (SAO). In some embodiment, the filtering operations includeadaptive loop filter (ALF).

FIG. 11 a illustrates portions of the video encoder 1000 that mayimplement MH mode for intra when encoding a block of pixels. Asillustrated, the video encoder 1000 implements a combined predictionmodule 1110, which produces the predicted pixel data 1013. The combinedprediction module 1110 receives intra-prediction values generated by theintra-picture prediction module 1025. The combined prediction module1110 also receives inter-prediction values from the motion compensationmodule 1030. The motion information and mode directions used forencoding a pixel block by the motion compensation module 1030 and theintra-picture prediction module 1025 are saved in a storage for use bythe same modules for subsequent blocks as candidates for merge mode orMH mode for intra.

A MH mode controller 1120 controls the operations of the intra-pictureprediction module 1025 and the motion compensation module 1030 when MHmode for Intra is enabled (for the block or a portion of the block). TheMH mode controller 1120 determines a list of inter-prediction modes(Candidate List I) and a list of intra-prediction modes (Candidate ListII). The candidates of each list are determined or identified based onvarious factors, including the size, width, or height of the currentblock, and/or a direction of a corresponding motion candidate. The MHmode controller 1120 may also enable or disable MH mode for intra basedon size, width, or height of the current block by enabling or disablingone or both of the intra prediction module 1025 and the motioncompensation module 1030. In some embodiments, the intra predictionmodule 1025 uses a buffer whose size is reduced based on a thresholdblock width or height of for disabling MH mode for intra.

The MH mode controller 1120 selects an inter-prediction candidate fromCandidate List I and an intra-prediction candidate from Candidate ListII. The motion compensation module 1030 performs inter-prediction basedon the candidate selected from Candidate List I. The intra-pictureprediction module 1025 performs intra prediction based on the candidateselected from Candidate List II. The results of the inter-prediction andintra-prediction are combined (e.g., averaged) at the combinedprediction module 1110 to generate the predicted pixel data 1013.

The MH mode controller also provides information to the entropy encoder1090 to insert into the bitstream as syntax elements. Such syntaxelements may signal whether MH mode for Intra is turned on. Such syntaxelements may also explicitly signal the selection of theinter-prediction and intra-prediction candidates from candidate lists Iand II for MH mode for intra. The syntax for signaling the selection ofthe inter-prediction and intra-prediction candidates may include onesingle index that selects the inter-prediction and intra-predictioncandidates from one combined list that includes both Candidate list Iand Candidate List II. The syntax for signaling the selection of theintra-prediction candidates and/or the inter-prediction candidate may beomitted (implicit signaling) if Candidate List I or Candidate List IIhas only one candidate.

The intra prediction module 1025 generates intra prediction result byusing the selected intra prediction mode to identify a set ofneighboring pixels and applying an interpolation filter to theidentified set of neighboring pixels to produce a set of interpolatedpixels. A signal (labeled as MH Intra/Normal Intra) controls whether theintra prediction module 1025 is used to generate intra prediction resultfor MH mode for intra or for normal intra prediction.

When the intra prediction module 1025 is used to produce intraprediction result for regular or normal intra prediction (i.e., not partof MH mode for intra, or described in section intra-prediction mode),tools for improving intra prediction such as PDPC and wide angular intraprediction may also be used. For example, when the selected intraprediction mode is planar mode, for normal intra prediction, the intraprediction module 1025 may also perform reference availability check andsubstitution, reference sample filtering, horizontal planar predictorgeneration and averaging, and PDPC.

On the other hand, when the intra prediction module 1025 is used togenerate intra prediction result for MH mode for intra, the intraprediction module 1025 performs a simplified intra prediction process.Such a simplified process may omit (at least some of) the filteringprocess, reduce the length of intra interpolation filter (e.g., havingthree or less taps instead of four taps), omit the tools for improvingintra prediction such as PDPC, and wide angular intra prediction, etc.The simplified intra prediction process may compute planar mode byapplying only a part (or a subset) or none of the four planar predictionsteps (reference availability check and substitution, reference samplefiltering, horizontal planar predictor generation and averaging, andPDPC). In some embodiments, the set of interpolated pixels is used asthe result of intra prediction without further improvement for MH modefor intra.

FIG. 11 b illustrates portions of the video encoder 1000 that mayimplement MH mode for Inter when encoding a block of pixels. Asillustrated, the video encoder 1000 implements the combined predictionmodule 1110, which produces the predicted pixel data 1013. The combinedprediction module 1110 receives a first set of inter-prediction valuesfrom the motion compensation module 1030. The combined prediction module1110 also receives a second set of inter-prediction values from the samemotion compensation module 1030, or a secondary motion compensationmodule 1130. The two sets of motion information used for encoding apixel block by the motion compensation module 1030 (and the secondarymotion compensation module 1130) are saved in a storage for use by thesame modules for subsequent blocks as candidates for merge mode or MHmode for inter.

The MH mode controller 1120 controls the operations of the motioncompensation module 1030 (and/or the secondary motion compensationmodule 1130) when MH mode for Inter is enabled (for the block or aportion of the block). The MH mode controller 1120 creates a list ofinter-prediction modes (Candidate List I). The candidates in the listare determined or identified based on various factors, including thesize, width, or height of the current block, and/or a direction of acorresponding motion candidate.

The MH mode controller 1120 selects a first inter-prediction candidateand a second inter-prediction candidate from Candidate List I. Themotion compensation module 1030 performs a first inter-prediction basedon the first inter-prediction candidate selected from Candidate List I.The motion compensation module 1030 (or the secondary motioncompensation module 1130) performs a second inter-prediction based onthe second inter-prediction candidate selected from Candidate List I.The results of the first inter-prediction and the secondinter-prediction are combined (e.g., averaged) at the combinedprediction module 1110 to generate the predicted pixel data 1013.

The MH mode controller also provides information to the entropy encoder1090 to insert into the bitstream as syntax elements. Such syntaxelements may signal whether MH mode for Inter is turned on. Such syntaxelements may also explicitly signal the selection of the firstinter-prediction and the second inter-prediction candidates fromCandidate list I for MH mode for inter. The syntax for signaling theselection of the first and second inter-prediction candidates mayinclude one single index that selects the first inter-predictioncandidates from Candidate List I and one single index that selects thesecond inter-prediction candidates from Candidate List I. The syntax forsignaling the selection of the first and second inter-predictioncandidates may include one single index that selects the twointer-prediction candidates from Candidate List I. The syntax forsignaling the selection of the inter-prediction candidates may beomitted (implicit signaling) if Candidate List I has only one candidate.

FIG. 12 conceptually illustrates a process 1200 that encodes a block ofpixels using MH mode for intra (or MH mode for inter). In someembodiments, one or more processing units (e.g., a processor) of acomputing device implementing the encoder 1000 performs the process 1200by executing instructions stored in a computer readable medium. In someembodiments, an electronic apparatus implementing the encoder 1000performs the process 1200.

The encoder receives (at step 1210) raw pixel or video data for a blockof pixels to be encoded as a current block of a current picture. Theencoder generates (at step 1220) a first prediction of the current blockbased on a first prediction mode that is selected from a first candidatelist. The first candidate list (e.g., Candidate List I) includes one ormore candidate inter-prediction modes. The first candidate list may bethe same as the merge candidate list, or a subset of the merge candidatelist.

The encoder determines (at step 1225) whether MH mode for Intra (or MHmode for inter) maybe enabled according to width, height, or other sizesettings of the current block. In some embodiments, the encoderdetermine whether to enable MH mode for Intra (or MH mode for inter)based on whether the size of the block meets (e.g., greater than orequal to) an enabling threshold (e.g., 64). The size of the block may bedetermined according to the height and/or width of the block (e.g.,area). If the size of the current block fails to meet (e.g., less than)the enabling threshold, the process proceeds to 1270. If the size of theblock meets the enabling threshold, the process proceeds to 1240. Insome embodiments, the encoder determines whether MH mode for Intra maybe disabled according to width and/or height of the block. In someembodiments, the encoder determine whether to disable MH mode for Intrabased on whether the width or the height of the block exceeds (e.g.,greater than) a disabling threshold (e.g., 64). If so, the processproceeds to 1270. If the width and/or height of the block does notexceed (e.g., less than or equal to) the disabling threshold, theprocess proceeds to 1240.

At step 1240, the encoder selects a second prediction mode from thefirst candidate list or a second candidate list that includes one ormore intra prediction modes. The encoder may identify candidates for thesecond candidate list (e.g., Candidate List II) based on a property ofthe block or a direction of the first prediction mode. For example, theordering of candidates in the second candidate list may be determinedbased on the direction of the first prediction mode (e.g., when themotion candidate for the first prediction mode is from the leftneighboring block, or the direction of the first intra-prediction modein the second candidate list is horizontal.). For another example, thenumber of candidates in the second candidate list may be determinedbased on a width, height, or size of the current block. In someembodiments, if there is only one candidate in the second candidatelist, the encoder selects the only candidate in the second candidatelist as the second prediction mode without signaling it explicitly inthe bitstream. The selection may be signaled by a code word that is tobe included in the bitstream as a syntax element. Different code wordsare assigned to different candidates in the second candidate list basedon the candidates' ordering in the list. The candidate that is first inthe list is assigned a shortest code word. The process then proceeds to1250.

At step 1250, the encoder generates a second prediction of the currentblock based on the selected second prediction mode by performing intraprediction. The encoder may omit tools that improves the result ofnormal intra prediction when performing intra prediction for MH mode forintra.

The encoder then encodes (at step 1260) the current block by using acombined prediction that is generated based on the first prediction andthe second prediction of the current block. The combined prediction maybe a weighted sum of the first prediction and the second prediction.

At step 1270, the encoder encodes the current block without using MHmode for Intra. In some embodiments, the current block is encoded byanother prediction mode, e.g., merge mode without combined prediction.In some other embodiments, the process 1200 may be modified for encodinga block of pixels using MH mode for inter, which should not be limitedin this disclosure.

Example Video Decoder

FIG. 13 illustrates an example video decoder 1300 that may implement MHmode (MH mode for intra and/or MH mode for inter). As illustrated, thevideo decoder 1300 is an image-decoding or video-decoding circuit thatreceives a bitstream 1395 and decodes the content of the bitstream intopixel data of video frames for display. The video decoder 1300 hasseveral components or modules for decoding the bitstream 1395, includingat least part of an inverse quantization module 1305, an inversetransform module 1310, an intra-prediction module 1325, a motioncompensation module 1330, an in-loop filter 1345, a decoded picturebuffer 1350, a MV buffer 1365, a MV prediction module 1375, and a parser1390. The motion compensation module 1330 is part of an inter-predictionmodule 1340.

In some embodiments, the modules 1310-1390 are modules of softwareinstructions being executed by one or more processing units (e.g., aprocessor) of a computing device. In some embodiments, the modules1310-1390 are modules of hardware circuits implemented by one or moreICs of an electronic apparatus. Though the modules 1310-1390 areillustrated as being separate modules, some of the modules can becombined into a single module.

The parser 1390 (or entropy decoder) receives the bitstream 1395 andperforms initial parsing according to the syntax defined by avideo-coding or image-coding standard. The parsed syntax elementincludes various header elements, flags, as well as quantized data (orquantized coefficients) 1312. The parser 1390 parses out the varioussyntax elements by using entropy-coding techniques such ascontext-adaptive binary arithmetic coding (CABAC) or Huffman encoding.

The inverse quantization module 1305 de-quantizes the quantized data (orquantized coefficients) 1312 to obtain transform coefficients, and theinverse transform module 1310 performs inverse transform on thetransform coefficients 1316 to produce reconstructed residual signal1319. The reconstructed residual signal 1319 is added with predictedpixel data 1313 from the intra-prediction module 1325 or the motioncompensation module 1330 to produce decoded pixel data 1317. The decodedpixels data are filtered by the in-loop filter 1345 and stored in thedecoded picture buffer 1350. In some embodiments, the decoded picturebuffer 1350 is a storage external to the video decoder 1300. In someembodiments, the decoded picture buffer 1350 is a storage internal tothe video decoder 1300.

The intra-prediction module 1325 receives intra-prediction data frombitstream 1395 and according to which, produces the predicted pixel data1313 from the decoded pixel data 1317 stored in the decoded picturebuffer 1350. In some embodiments, the decoded pixel data 1317 is alsostored in a line buffer (not illustrated) for intra-picture predictionand spatial MV prediction.

In some embodiments, the content of the decoded picture buffer 1350 isused for display. A display device 1355 either retrieves the content ofthe decoded picture buffer 1350 for display directly or retrieves thecontent of the decoded picture buffer to a display buffer. In someembodiments, the display device receives pixel values from the decodedpicture buffer 1350 through a pixel transport.

The motion compensation module 1330 produces predicted pixel data 1313from the decoded pixel data 1317 stored in the decoded picture buffer1350 according to motion compensation MVs (MC MVs). These motioncompensation MVs are decoded by adding the residual motion data receivedfrom the bitstream 1395 with predicted MVs received from the MVprediction module 1375.

The MV prediction module 1375 generates the predicted MVs based onreference MVs that were generated for decoding previous video frames,e.g., the motion compensation MVs that were used to perform motioncompensation. The MV prediction module 1375 retrieves the reference MVsof previous video frames from the MV buffer 1365. The video decoder 1300stores the motion compensation MVs generated for decoding the currentvideo frame in the MV buffer 1365 as reference MVs for producingpredicted MVs.

The in-loop filter 1345 performs filtering or smoothing operations onthe decoded pixel data 1317 to reduce the artifacts of coding,particularly at boundaries of pixel blocks. In some embodiments, thefiltering operation performed includes deblocking and/or sample adaptiveoffset (SAO). In some embodiment, the filtering operations includeadaptive loop filter (ALF).

FIG. 14 a illustrates portions of the video decoder 1300 that mayimplement MH mode for Intra when decoding a block of pixels. Asillustrated, the video decoder 1300 implements a combined predictionmodule 1410, which produces the predicted pixel data 1313. The combinedprediction module 1410 receives intra-prediction values generated by theintra-picture prediction module 1325. The combined prediction module1410 also receives inter-prediction values from the motion compensationmodule 1330. The motion information and mode directions used fordecoding a pixel block by the motion compensation module 1330 and theintra-picture prediction module 1325 are saved in a storage for use bythe same modules for subsequent blocks as candidates for merge mode orMH mode.

A MH mode controller 1420 controls the operations of the intra-pictureprediction module 1325 and the motion compensation module 1330 when MHmode for Intra is enabled (for the block or a portion of the block). TheMH mode controller 1420 determines a list of inter-prediction modes(Candidate List I) and a list of intra-prediction modes (Candidate ListII). The candidates of each list are determined or identified based onvarious factors, including the size, width, or height of the currentblock, and/or a direction of a corresponding motion candidate. The MHmode controller 1420 may also enable or disable MH mode for intra basedon size, width, or height of the current block by enabling or disablingone or both of the intra prediction module 1325 and the motioncompensation module 1330. In some embodiments, the intra predictionmodule 1325 uses a buffer whose size is reduced based on a thresholdblock width or height of for disabling MH mode for intra.

The MH mode controller 1420 selects an inter-prediction candidate fromCandidate List I and an intra-prediction candidate from Candidate ListII. The motion compensation module 1330 performs inter-prediction basedon the candidate selected from Candidate List I. The intra-pictureprediction module 1325 performs intra prediction based on the candidateselected from Candidate List II. The results of the inter-prediction andintra-prediction are combined (e.g., averaged) at the combinedprediction module 1410 to generate the predicted pixel data 1313.

The MH mode controller 1420 receives information from the parser 1390based on syntax elements in the bitstream. Such syntax elements maysignal whether MH mode for intra is turned on. Such syntax elements mayalso explicitly signal the selection of the inter-prediction andintra-prediction candidates from candidate lists I and II for MH modefor intra. The syntax for signaling the selection of theinter-prediction and intra-prediction candidates may include one singleindex that selects the inter-prediction candidates from Candidate List Iand one single index that selects the intra-prediction candidates fromCandidate List II. The syntax for signaling the selection of theinter-prediction and intra-prediction candidates may include one singleindex that selects the inter-prediction and intra-prediction candidatesfrom one combined list that includes both candidates list I andCandidate List II. The syntax for signaling the selection of theintra-prediction candidates and/or the inter-prediction candidate may beomitted (implicit signaling) if Candidate List I or Candidate List IIhas only one candidate.

The intra prediction module 1325 generates intra prediction result byusing the selected intra prediction mode to identify a set ofneighboring pixels and applying an interpolation filter to theidentified set of neighboring pixels to produce a set of interpolatedpixels. A signal (labeled as MH Intra/Normal Intra) controls whether theintra prediction module 1325 is used to generate intra prediction resultfor MH mode for intra or for normal intra prediction.

When the intra prediction module 1325 is used to produce intraprediction result for regular or normal intra prediction (i.e., not partof MH mode for intra), tools for improving intra prediction such as PDPCand wide angular intra prediction may also be used. For example, whenthe selected intra prediction mode is planar mode, for normal intraprediction, the intra prediction module 1325 may also perform referenceavailability check and substitution, reference sample filtering,horizontal planar predictor generation and averaging, and PDPC.

On the other hand, when the intra prediction module 1325 is used togenerate intra prediction result for MH mode for intra, the intraprediction module 1325 uses a simplified intra prediction process. Sucha simplified process may omit (at least some of) the filtering process,reduce the length of intra interpolation filter (e.g., having three orless taps instead of four taps), omit the tools for improving intraprediction such as PDPC, and wide angular intra prediction, etc. Thesimplified intra prediction process may compute planar mode by applyingonly a part (or a subset) or none of the four planar prediction steps(reference availability check and substitution, reference samplefiltering, horizontal planar predictor generation and averaging, andPDPC). In some embodiments, the set of interpolated pixels is used asthe result of intra prediction without further improvement for MH modefor intra.

FIG. 14 b illustrates portions of the video decoder 1300 that mayimplement MH mode for Inter when decoding a block of pixels. Asillustrated, the video decoder 1300 implements a combined predictionmodule 1410, which produces the predicted pixel data 1313. The combinedprediction module 1410 receives a first set of inter-prediction valuesfrom the motion compensation module 1330. The combined prediction module1410 also receives a second set of inter-prediction values from the samemotion compensation module 1330, or a secondary motion compensationmodule 1430. The two sets of motion information used for encoding apixel block by the motion compensation module 1330 (and the secondarymotion compensation module 1430) are saved in a storage for use by thesame modules for subsequent blocks as candidates for merge mode or MHmode for inter.

The MH mode controller 1420 controls the operations of the motioncompensation module 1330 (and/or the secondary motion compensationmodule 1430) when MH mode for Inter is enabled (for the block or aportion of the block). The MH mode controller 1420 creates a list ofinter-prediction modes (Candidate List I). The candidates in the listare determined or identified based on various factors, including thesize, width, or height of the current block, and/or a direction of acorresponding motion candidate (If the motion candidate is from the leftneighboring block, the direction is horizontal).

The MH mode controller 1420 selects a first inter-prediction candidateand a second inter-prediction candidate from Candidate List I. Themotion compensation module 1330 performs a first inter-prediction basedon the first inter-prediction candidate selected from Candidate List I.The same motion compensation module 1330 (or the secondary motioncompensation module 1430) performs a second inter-prediction based onthe second inter-prediction candidate selected from Candidate List I.The results of the first inter-prediction and the secondinter-prediction are combined (e.g., averaged) at the combinedprediction module 1410 to generate the predicted pixel data 1313.

The MH mode controller receives information parsed by the entropydecoder 1390 from syntax elements in the bitstream. Such syntax elementsmay signal whether MH mode for Inter is turned on. Such syntax elementsmay also explicitly signal the selection of the first inter-predictionand the second inter-prediction candidates from Candidate list I for MHmode for inter. The syntax for signaling the selection of the first andsecond inter-prediction candidates may include one single index thatselects the two inter-prediction candidates from Candidate List I. Thesyntax for signaling the selection of the inter-prediction candidatesmay be omitted (implicit signaling) if Candidate List I has only onecandidate.

FIG. 15 conceptually illustrates a process 1500 that decodes a block ofpixels using MH mode for Intra (or MH mode for Inter). In someembodiments, one or more processing units (e.g., a processor) of acomputing device implementing the decoder 1300 performs the process 1500by executing instructions stored in a computer readable medium. In someembodiments, an electronic apparatus implementing the decoder 1300performs the process 1500.

The decoder receives (at step 1510) to-be-decoded data for a block ofpixels to be decoded as a current block of a current picture. Thedecoder generates (at step 1520) a first prediction of the current blockbased on a first prediction mode that is selected from a first candidatelist. The first candidate list (e.g., Candidate List I) includes one ormore candidate inter-prediction modes. The first candidate list may bethe same as the merge candidate list, or a subset of the merge candidatelist.

The decoder determines (at step 1525) whether MH mode for Intra (or MHmode for inter) maybe enabled according to width, height, or other sizesettings of the current block. In some embodiments, the decoderdetermine whether to enable MH mode for Intra (or MH mode for inter)based on whether the size of the block meets (e.g., greater than orequal to) an enabling threshold (e.g., 64). The size of the block may bedetermined according to the height and/or width of the block (e.g.,area). If the size of the current block fails to meet (e.g., less than)the enabling threshold, the process proceeds to 1570. If the size of theblock meets the enabling threshold, the process proceeds to 1540. Insome embodiments, the decoder determines whether MH mode for Intra maybe disabled according to width and/or height of the block. In someembodiments, the decoder determine whether to disable MH mode for Intrabased on whether the width or the height of the block exceeds (e.g.,greater than) a disabling threshold (e.g., 64). If so, the processproceeds to 1570. If the width and/or height of the block does notexceed (e.g., less than or equal to) the disabling threshold, theprocess proceeds to 1540.

At step 1540, the decoder selects a second prediction mode from thefirst candidate list or a second candidate list that includes one ormore intra prediction modes. The decoder may identify candidates for thesecond candidate list (e.g., Candidate List II) based on a property ofthe block or a direction of the first prediction mode. For example, theordering of candidates in the second candidate list may be determinedbased on the direction of the first prediction mode (e.g., when themotion candidate for the first prediction mode is from the leftneighboring block, or the direction of the first intra-prediction modein the second candidate list is horizontal.). For another example, thenumber of candidates in the second candidate list may be determinedbased on a width, height, or size of the current block. In someembodiments, if there is only one candidate in the second candidatelist, the decoder selects the only candidate in the second candidatelist as the second prediction mode without signaling it explicitly inthe bitstream. The selection may be signaled by a code word that is tobe included in the bitstream as a syntax element. Different code wordsare assigned to different candidates in the second candidate list basedon the candidates' ordering in the list. The candidate that is first inthe list is assigned a shortest code word. The process then proceeds to1550.

At step 1550, the decoder generates a second prediction of the currentblock based on the selected second prediction mode by performing intraprediction. The decoder may omit tools that improves the result ofnormal intra prediction when performing intra prediction for MH mode forintra.

The decoder then reconstructs (at step 1560) the current block by usinga combined prediction that is generated based on the first predictionand the second prediction of the current block. The combined predictionmay be a weighted sum of the first prediction and the second prediction.

At step 1570, the decoder reconstructs the current block without usingMH mode for Intra. In some embodiments, the current block is decoded byanother prediction mode, e.g., merge mode without combined prediction.In some other embodiments, the process 1500 may be modified for decodinga block of pixels using MH mode for Inter, which should not be limitedin this disclosure.

Example Electronic System

Many of the above-described features and applications are implemented assoftware processes that are specified as a set of instructions recordedon a computer readable storage medium (also referred to as computerreadable medium). When these instructions are executed by one or morecomputational or processing unit(s) (e.g., one or more processors, coresof processors, or other processing units), they cause the processingunit(s) to perform the actions indicated in the instructions. Examplesof computer readable media include, but are not limited to, CD-ROMs,flash drives, random-access memory (RAM) chips, hard drives, erasableprogrammable read only memories (EPROMs), electrically erasableprogrammable read-only memories (EEPROMs), etc. The computer readablemedia does not include carrier waves and electronic signals passingwirelessly or over wired connections.

In this specification, the term “software” is meant to include firmwareresiding in read-only memory or applications stored in magnetic storagewhich can be read into memory for processing by a processor. Also, insome embodiments, multiple software inventions can be implemented assub-parts of a larger program while remaining distinct softwareinventions. In some embodiments, multiple software inventions can alsobe implemented as separate programs. Finally, any combination ofseparate programs that together implement a software invention describedhere is within the scope of the present disclosure. In some embodiments,the software programs, when installed to operate on one or moreelectronic systems, define one or more specific machine implementationsthat execute and perform the operations of the software programs.

FIG. 16 conceptually illustrates an electronic system 1600 with whichsome embodiments of the present disclosure are implemented. Theelectronic system 1600 may be a computer (e.g., a desktop computer,personal computer, tablet computer, etc.), phone, PDA, or any other sortof electronic device. Such an electronic system includes various typesof computer readable media and interfaces for various other types ofcomputer readable media. Electronic system 1600 includes a bus 1605,processing unit(s) 1610, a graphics-processing unit (GPU) 1615, a systemmemory 1620, a network 1625, a read-only memory 1630, a permanentstorage device 1635, input devices 1640, and output devices 1645.

The bus 1605 collectively represents all system, peripheral, and chipsetbuses that communicatively connect the numerous internal devices of theelectronic system 1600. For instance, the bus 1605 communicativelyconnects the processing unit(s) 1610 with the GPU 1615, the read-onlymemory 1630, the system memory 1620, and the permanent storage device1635.

From these various memory units, the processing unit(s) 1610 retrievesinstructions to execute and data to process in order to execute theprocesses of the present disclosure. The processing unit(s) may be asingle processor or a multi-core processor in different embodiments.Some instructions are passed to and executed by the GPU 1615. The GPU1615 can offload various computations or complement the image processingprovided by the processing unit(s) 1610.

The read-only-memory (ROM) 1630 stores static data and instructions thatare used by the processing unit(s) 1610 and other modules of theelectronic system. The permanent storage device 1635, on the other hand,is a read-and-write memory device. This device is a non-volatile memoryunit that stores instructions and data even when the electronic system1600 is off. Some embodiments of the present disclosure use amass-storage device (such as a magnetic or optical disk and itscorresponding disk drive) as the permanent storage device 1635.

Other embodiments use a removable storage device (such as a floppy disk,flash memory device, etc., and its corresponding disk drive) as thepermanent storage device. Like the permanent storage device 1635, thesystem memory 1620 is a read-and-write memory device. However, unlikestorage device 1635, the system memory 1620 is a volatile read-and-writememory, such a random access memory. The system memory 1620 stores someof the instructions and data that the processor uses at runtime. In someembodiments, processes in accordance with the present disclosure arestored in the system memory 1620, the permanent storage device 1635,and/or the read-only memory 1630. For example, the various memory unitsinclude instructions for processing multimedia clips in accordance withsome embodiments. From these various memory units, the processingunit(s) 1610 retrieves instructions to execute and data to process inorder to execute the processes of some embodiments.

The bus 1605 also connects to the input and output devices 1640 and1645. The input devices 1640 enable the user to communicate informationand select commands to the electronic system. The input devices 1640include alphanumeric keyboards and pointing devices (also called “cursorcontrol devices”), cameras (e.g., webcams), microphones or similardevices for receiving voice commands, etc. The output devices 1645display images generated by the electronic system or otherwise outputdata. The output devices 1645 include printers and display devices, suchas cathode ray tubes (CRT) or liquid crystal displays (LCD), as well asspeakers or similar audio output devices. Some embodiments includedevices such as a touchscreen that function as both input and outputdevices.

Finally, as shown in FIG. 16 , bus 1605 also couples electronic system1600 to a network 1625 through a network adapter (not shown). In thismanner, the computer can be a part of a network of computers (such as alocal area network (“LAN”), a wide area network (“WAN”), or an Intranet,or a network of networks, such as the Internet. Any or all components ofelectronic system 1600 may be used in conjunction with the presentdisclosure.

Some embodiments include electronic components, such as microprocessors,storage and memory that store computer program instructions in amachine-readable or computer-readable medium (alternatively referred toas computer-readable storage media, machine-readable media, ormachine-readable storage media). Some examples of such computer-readablemedia include RAM, ROM, read-only compact discs (CD-ROM), recordablecompact discs (CD-R), rewritable compact discs (CD-RW), read-onlydigital versatile discs (e.g., DVD-ROM, dual-layer DVD-ROM), a varietyof recordable/rewritable DVDs (e.g., DVD-RAM, DVD-RW, DVD+RW, etc.),flash memory (e.g., SD cards, mini-SD cards, micro-SD cards, etc.),magnetic and/or solid state hard drives, read-only and recordableBlu-Ray® discs, ultra-density optical discs, any other optical ormagnetic media, and floppy disks. The computer-readable media may storea computer program that is executable by at least one processing unitand includes sets of instructions for performing various operations.Examples of computer programs or computer code include machine code,such as is produced by a compiler, and files including higher-level codethat are executed by a computer, an electronic component, or amicroprocessor using an interpreter.

While the above discussion primarily refers to microprocessor ormulti-core processors that execute software, many of the above-describedfeatures and applications are performed by one or more integratedcircuits, such as application specific integrated circuits (ASICs) orfield programmable gate arrays (FPGAs). In some embodiments, suchintegrated circuits execute instructions that are stored on the circuititself. In addition, some embodiments execute software stored inprogrammable logic devices (PLDs), ROM, or RAM devices.

As used in this specification and any claims of this application, theterms “computer”, “server”, “processor”, and “memory” all refer toelectronic or other technological devices. These terms exclude people orgroups of people. For the purposes of the specification, the termsdisplay or displaying means displaying on an electronic device. As usedin this specification and any claims of this application, the terms“computer readable medium,” “computer readable media,” and “machinereadable medium” are entirely restricted to tangible, physical objectsthat store information in a form that is readable by a computer. Theseterms exclude any wireless signals, wired download signals, and anyother ephemeral signals.

While the present disclosure has been described with reference tonumerous specific details, one of ordinary skill in the art willrecognize that the present disclosure can be embodied in other specificforms without departing from the spirit of the present disclosure. Inaddition, a number of the figures (including FIGS. 12 and 15 )conceptually illustrate processes. The specific operations of theseprocesses may not be performed in the exact order shown and described.The specific operations may not be performed in one continuous series ofoperations, and different specific operations may be performed indifferent embodiments. Furthermore, the process could be implementedusing several sub-processes, or as part of a larger macro process. Thus,one of ordinary skill in the art would understand that the presentdisclosure is not to be limited by the foregoing illustrative details,but rather is to be defined by the appended claims.

Additional Notes

The herein-described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely examples, and that in fact many other architectures can beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermediate components. Likewise, any two componentsso associated can also be viewed as being “operably connected”, or“operably coupled”, to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable”, to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically mateable and/or physically interactingcomponents and/or wirelessly interactable and/or wirelessly interactingcomponents and/or logically interacting and/or logically interactablecomponents.

Further, with respect to the use of substantially any plural and/orsingular terms herein, those having skill in the art can translate fromthe plural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

Moreover, it will be understood by those skilled in the art that, ingeneral, terms used herein, and especially in the appended claims, e.g.,bodies of the appended claims, are generally intended as “open” terms,e.g., the term “including” should be interpreted as “including but notlimited to,” the term “having” should be interpreted as “having atleast,” the term “includes” should be interpreted as “includes but isnot limited to,” etc. It will be further understood by those within theart that if a specific number of an introduced claim recitation isintended, such an intent will be explicitly recited in the claim, and inthe absence of such recitation no such intent is present. For example,as an aid to understanding, the following appended claims may containusage of the introductory phrases “at least one” and “one or more” tointroduce claim recitations. However, the use of such phrases should notbe construed to imply that the introduction of a claim recitation by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim recitation to implementations containing only onesuch recitation, even when the same claim includes the introductoryphrases “one or more” or “at least one” and indefinite articles such as“a” or “an,” e.g., “a” and/or “an” should be interpreted to mean “atleast one” or “one or more;” the same holds true for the use of definitearticles used to introduce claim recitations. In addition, even if aspecific number of an introduced claim recitation is explicitly recited,those skilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number, e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations. Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,etc.” is used, in general such a construction is intended in the senseone having skill in the art would understand the convention, e.g., “asystem having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc. In those instances where a convention analogous to “atleast one of A, B, or C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention, e.g., “a system having at least one of A, B, or C” wouldinclude but not be limited to systems that have A alone, B alone, Calone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc. It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

From the foregoing, it will be appreciated that various implementationsof the present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various implementations disclosed herein are notintended to be limiting, with the true scope and spirit being indicatedby the following claims.

What is claimed is:
 1. A video decoding method comprising: receivingto-be-decoded data from a bitstream for a block of pixels to be decodedas a current block of a current picture of a video; generating a firstprediction of the current block based on an inter prediction mode;determining a block size of the current block according to a width, aheight, or both of the current block; performing: disabling a combinedprediction mode for the current block responsive to the width or theheight of the current block being greater than a threshold length; orenabling the combined prediction mode for the current block responsiveto the width and the height of the current block being not greater thanthe threshold length; and when the combined prediction mode is enabled:generating a second prediction of the current block based on an intraprediction mode; generating a combined prediction for the current blockbased on the first prediction and the second prediction; andreconstructing the current block by using the combined prediction,wherein: the inter prediction mode is selected from a first candidatelist having one or more inter prediction candidates, the first candidatelist corresponding to a merging candidate list that includes at leastone history-based merging candidate selected from a history-based motionvector predictor (HMVP) candidate list, and the intra prediction mode isinferred as a planar mode without parsing a syntax to indicate the intraprediction mode.
 2. The method of claim 1, wherein the one or more interprediction candidates of the first candidate list are identical to oneor more candidates of a merge candidate list of the current block. 3.The method of claim 1, wherein the intra prediction mode is inferredwithout at least one of (i) reference availability check andsubstitution, (ii) reference sample filtering, (iii) horizontal planarpredictor generation and averaging, and (iv) position dependent intraprediction combination (PDPC).
 4. The method of claim 1, wherein thesecond prediction is generated without using position dependent intraprediction combination (PDPC) or angular intra prediction.
 5. The methodof claim 1, wherein the threshold length is
 64. 6. The method of claim1, wherein the HMVP candidate list is emptied responsive to the currentblock being a first block of a slice of the current picture.
 7. A videoencoding method comprising: receiving raw pixel data for a block ofpixels to be encoded as a current block of a current picture of a videointo a bitstream; generating a first prediction of the current blockbased on an inter prediction mode; determining a block size of thecurrent block according to a width, a height, or both of the currentblock; performing: disabling a combined prediction mode for the currentblock responsive to the width or the height of the current block beinggreater than a threshold length; or enabling the combined predictionmode for the current block responsive to the width and the height of thecurrent block being not greater than the threshold length; and when thecombined prediction mode is enabled: generating a second prediction ofthe current block based on an intra prediction mode; generating acombined prediction for the current block based the first prediction andthe second prediction; and encoding the current block into the bitstreamby using the combined prediction, wherein: the inter prediction mode isselected from a first candidate list having one or more inter predictioncandidates, the first candidate list corresponding to a mergingcandidate list that includes at least one history-based mergingcandidate selected from a history-based motion vector predictor (HMVP)candidate list, and the intra prediction mode is inferred as a planarmode without parsing a syntax to indicate the intra prediction mode. 8.An electronic apparatus comprising: a video decoder circuit configuredto perform operations comprising: receiving to-be-decoded data from afirst bitstream for a first block of pixels to be decoded as a firstcurrent block of a first current picture of a first video; generating afirst prediction of the first current block based on an inter predictionmode; determining a block size of the first current block according to awidth, a height, or both of the first current block; performing:disabling a combined prediction mode for the first current blockresponsive to the width or the height of the first current block beinggreater than a threshold length; or enabling the combined predictionmode for the first current block responsive to the width and the heightof the first current block being not greater than the threshold length;and when the combined prediction mode is enabled: generating a secondprediction of the first current block based on an intra prediction mode;generating a first combined prediction for the first current block basedon the first prediction and the second prediction thereof; andreconstructing the first current block by using the first combinedprediction; and a video encoder circuit configured to perform operationscomprising: receiving raw pixel data for a second block of pixels to beencoded as a second current block of a second current picture of asecond video into a second bitstream; generating a first prediction ofthe second current block based on the inter prediction mode; determininga block size of the second current block according to a width, a height,or both of the second current block; performing: disabling the combinedprediction mode for the second current block responsive to the width orthe height of the second current block being greater than the thresholdlength; or enabling the combined prediction mode for the second currentblock responsive to the width and the height of the second current blockbeing not greater than the threshold length; and when the combinedprediction mode is enabled: generating a second prediction of the secondcurrent block based on the intra prediction mode; generating a secondcombined prediction for the second current block based on the firstprediction and the second prediction thereof; and encoding the secondcurrent block into the second bitstream by using the second combinedprediction, wherein: the inter prediction mode is selected from a firstcandidate list having one or more inter prediction candidates, the firstcandidate list corresponding to a merging candidate list that includesat least one history-based merging candidate selected from ahistory-based motion vector predictor (HMVP) candidate list, and theintra prediction mode is inferred as a planar mode without parsing asyntax to indicate the intra prediction mode.
 9. A video coding methodcomprising: receiving data to be encoded or decoded as a current blockof a current picture of a video; generating a first prediction of thecurrent block based on an inter prediction mode; determining a blocksize of the current block according to a width, a height, or both of thecurrent block; performing: disabling a combined prediction mode for thecurrent block responsive to the width or the height of the current blockbeing greater than a threshold length; or enabling the combinedprediction mode for the current block responsive to the width and theheight of the current block being not greater than a threshold length;and when the combined prediction mode is enabled: generating a secondprediction of the current block based on an intra prediction mode;generating a combined prediction for the current block based on thefirst prediction and the second prediction; and using the combinedprediction to reconstruct the current block or to encode the currentblock into a bitstream, wherein: the inter prediction mode is selectedfrom a first candidate list having one or more inter predictioncandidates, the first candidate list corresponding to a mergingcandidate list that includes at least one history-based mergingcandidate selected from a history-based motion vector predictor (HMVP)candidate list, and the intra prediction mode is inferred as a planarmode without parsing a syntax to indicate the intra prediction mode.